Laboratory Studies
In a healthy patient with no other abnormalities, laboratory investigation is generally not necessary. A small subset of patients with aural atresia will have 18q chromosome deletion syndrome. These children typically have normal auricles with complete atresia of the ear canal. Genetic testing can identify this rare condition. [9, 26]
Imaging Studies
Thin section (≤1-mm sections), high-resolution, axial and coronal computed tomography (CT) of the temporal bone is the study of choice in the surgical workup and evaluation of patients with congenital aural atresia (CAA). Given the radiation exposure of this imaging modality, the CT scan is not recommended until the child is being considered for surgery, around the age of 5-6 years.
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Perform the study by obtaining contiguous images with a thickness of 1 mm or less (submillimeter thickness) in both axial and coronal planes (coronal reconstruction is adequate with the appropriate software).
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Imaging provides information on whether surgical repair is feasible based on the anatomy present.
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Obtain imaging when surgical correction is contemplated or just before surgery.
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As long as audiologic evidence reveals that the inner ear is functional, imaging is not necessary during early infancy and childhood.
In 1992, Jahrsdoerfer et al developed a 10-point grading system to determine surgical candidacy based on key features from the CT scan and the appearance of the external ear. [19] This scheme is also used to indirectly estimate the likelihood of success if surgical correction is performed. [27]
Jahrsdoerfer recommends operating on unilateral patients with scores of 7 or higher; bilateral patients with a grade 5-6 or higher. This system bases surgical success on a postoperative speech-reception threshold (SRT) of less than or equal to 30 dB HL, which, depending on the anatomy, is attainable in over 80% of patients. [27] As a reflection of the conservative nature of this grading system, a score of 10 is never given.
The following is a summary of this 10-point grading system:
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Stapes present = 2 points
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Oval window open = 1 point
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Middle ear space = 1 point
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Facial nerve = 1 point
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Malleus-incus complex = 1 point
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Mastoid pneumatization = 1 point
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Incus-stapes connection = 1 point
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Round window = 1 point
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External ear appearance = 1 point
Each ear is given a grade based on the CT-scan anatomy and this scale. The anatomy predicts the candidacy of that ear for atresia surgery. Of patients with scores of 7 or greater, 80-90% have been shown to achieve normal or near-normal hearing (≤30 dB HL speech reception threshold), whereas only 40-45% of patients with a score below 7 will achieve a good hearing result. [27]
Other Tests
Audiometry is equally as important as imaging in the evaluation of the patient with CAA. Air and bone conduction pure-tone thresholds at 250 Hz, 500 Hz, 1000 Hz, 2000 Hz, 4000 Hz, 6000 Hz, and 8000 Hz, speech reception thresholds, and speech discrimination scores comprise the routine audiological assessment. Air conduction thresholds in the atretic ear tend to run in the 60-70 dB HL range with similar speech reception thresholds. Bone conduction thresholds in the atretic ear are typically in the normal range (and if they are not, the patient may not be a candidate for surgery), with excellent speech discrimination scores.
The masking dilemma arises when testing the patient with bilateral CAA. How does the audiologist establish bone conduction thresholds for each ear in bilateral CAA? The sensorineural acuity level test (SAL) allows the establishment of individual bone conduction thresholds in bilateral CAA, as follows:
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Determine patient's thresholds through earphones to 500, 1000, 2000, and 4000 Hz.
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Place a bone oscillator on the forehead and present masking through it at the following intensities:
500 Hz - 50 dB HL
1000 Hz - 50 dB HL
2000 Hz - 60 dB HL
4000 Hz - 60 dB HL
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With masking present, reestablish air conduction thresholds.
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At each frequency, determine the difference between the masked air conduction threshold and the unmasked air conduction threshold
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Norms of threshold shift with bone conduction masking are as follows:
500 Hz - 40 dB HL
1000 Hz - 50 dB HL
2000 Hz - 45 dB HL
4000 Hz - 50 dB HL
If the masked threshold shifts more than the norm, the bone conduction threshold is 0 dB HL. If the masked threshold shifts less than the norm, then the bone conduction threshold is the difference between the norm and the amount of shift (eg, if the norm is 50 and the amount of shift is 30, the masked bone conduction is 20).
Diagnostic Procedures
See discussion of audiology and CT temporal bone imaging above.
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Grade III microtia with complete absence (atresia) of the external auditory canal.
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Appearance of surgically-corrected microtia with complete atresia of the external ear canal.
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Axial CT scan in a patient with congenital aural atresia (CAA). Note the atretic plate just lateral to the ossicles.
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Coronal CT scan of left temporal bone in a patient with congenital aural atresia (CAA). Note absence of the ear canal. The atretic plate may be seen just lateral to the ossicles.
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Three-dimensional reconstructed CT scan of lateral skull in a child with aural atresia. Note the absence of a bony aperture (external ear canal) on the side of the left temporal bone.
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Coronal CT scan of patient with ear canal cholesteatoma (right ear) in the setting of congenital aural stenosis. Note the rounded edges of ear canal bone filled with soft tissue density extending into the middle ear.
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Very low tegmen (bone that separates brain from ear) and lack of middle ear aeration make this patient not a candidate for atresia surgery.
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Intraoperative photograph of a newly drilled ear canal, middle ear space, and ossicular chain in a patient with congenital aural atresia (CAA).
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Intraoperative image of the bony landmarks used to identify the site for drilling the bony canal in a right ear - zygomatic root, glenoid fossa, mastoid tip. Patient in the surgical position.
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Intraoperative image of a left ear in the surgical position upon entering the middle ear in the epitympanum. The fused malleus-incus complex can be seen.
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Intraoperative image of a right ear with a lateral facial nerve identified in the mastoid segment.
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Intraoperative image of the right ear with the fascia graft draped over the ossicular chain
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Intraoperative image of a right ear with the skin graft placed in position
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Intraoperative image of a right ear meatoplasty.
